// Info: The idea about the ring buffer is that we have a FIFO
// buffer where we store all incomming messages requested by
// operators.
// Each message in process or waiting to be processed will be
// stored in a DB. When the processing of a given message is
// done it will be removed from the state db, and an entry will
// made in the persistent message log.

package steward

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"sync"
	"time"

	copier "github.com/jinzhu/copier"
	bolt "go.etcd.io/bbolt"
)

// samValue represents one message with a subject. This
// struct type is used when storing and retreiving from
// db.
type samDBValue struct {
	ID  int
	SAM subjectAndMessage
}

// ringBuffer holds the data of the buffer,
type ringBuffer struct {
	// In memory buffer for the messages.
	bufData chan samDBValue
	// The database to use.
	db               *bolt.DB
	samValueBucket   string
	indexValueBucket string
	// The current number of items in the database.
	totalMessagesIndex int
	mu                 sync.Mutex
	// The channel to send messages that have been processed,
	// and we want to store it in the permanent message log.
	permStore chan string
	// Name of node.
	nodeName Node
	// ringBufferBulkInCh from *server are also implemented here,
	// so the ringbuffer can send it's error messages the same
	// way as all messages are handled.
	ringBufferBulkInCh chan []subjectAndMessage
	metrics            *metrics
	configuration      *Configuration
	errorKernel        *errorKernel
	processInitial     process
}

// newringBuffer returns a push/pop storage for values.
func newringBuffer(ctx context.Context, metrics *metrics, configuration *Configuration, size int, dbFileName string, nodeName Node, ringBufferBulkInCh chan []subjectAndMessage, samValueBucket string, indexValueBucket string, errorKernel *errorKernel, processInitial process) *ringBuffer {

	r := ringBuffer{}

	// Check if socket folder exists, if not create it
	if _, err := os.Stat(configuration.DatabaseFolder); os.IsNotExist(err) {
		err := os.MkdirAll(configuration.DatabaseFolder, 0770)
		if err != nil {
			log.Printf("error: failed to create database directory %v: %v\n", configuration.DatabaseFolder, err)
			os.Exit(1)
		}
	}

	DatabaseFilepath := filepath.Join(configuration.DatabaseFolder, dbFileName)

	// ---
	var db *bolt.DB
	if configuration.RingBufferPersistStore {
		var err error
		db, err = bolt.Open(DatabaseFilepath, 0660, nil)
		if err != nil {
			log.Printf("error: failed to open db: %v\n", err)
			os.Exit(1)
		}
	}

	r.bufData = make(chan samDBValue, size)
	r.db = db
	r.samValueBucket = samValueBucket
	r.indexValueBucket = indexValueBucket
	r.permStore = make(chan string)
	r.nodeName = nodeName
	r.ringBufferBulkInCh = ringBufferBulkInCh
	r.metrics = metrics
	r.configuration = configuration
	r.processInitial = processInitial

	return &r
}

// start will process incomming messages through the inCh,
// put the messages on a buffered channel
// and deliver messages out when requested on the outCh.
func (r *ringBuffer) start(ctx context.Context, inCh chan subjectAndMessage, outCh chan samDBValueAndDelivered) {

	// Starting both writing and reading in separate go routines so we
	// can write and read concurrently.

	r.totalMessagesIndex = 0
	if r.configuration.RingBufferPersistStore {
		r.totalMessagesIndex = r.getIndexValue()
	}

	// Fill the buffer when new data arrives into the system
	go r.fillBuffer(ctx, inCh)

	// Start the process to permanently store done messages.
	go r.startPermanentStore(ctx)

	// Start the process that will handle messages present in the ringbuffer.
	go r.processBufferMessages(ctx, outCh)

	go func() {
		ticker := time.NewTicker(time.Second * 5)
		defer ticker.Stop()

		for {
			select {
			case <-ticker.C:
				if r.configuration.RingBufferPersistStore {
					r.dbUpdateMetrics(r.samValueBucket)
				}
			case <-ctx.Done():
				return
			}
		}
	}()
}

// fillBuffer will fill the buffer in the ringbuffer  reading from the inchannel.
// It will also store the messages in a K/V DB while being processed.
func (r *ringBuffer) fillBuffer(ctx context.Context, inCh chan subjectAndMessage) {
	// At startup get all the values that might be in the K/V store so we can
	// put them into the buffer before we start to fill up with new incomming
	// messages to the system.
	// This is needed when the program have been restarted, and we need to check
	// if there where previously unhandled messages that need to be handled first.

	if r.configuration.RingBufferPersistStore {
		func() {
			s, err := r.dumpBucket(r.samValueBucket)
			if err != nil {
				er := fmt.Errorf("info: fillBuffer: retreival of values from k/v store failed, probaly empty database, and no previous entries in db to process: %v", err)
				log.Printf("%v\n", er)
				return
			}

			for _, v := range s {
				r.bufData <- v
			}
		}()
	}

	// Check for incomming messages. These are typically comming from
	// the go routine who reads the socket.
	for {
		select {
		case sam := <-inCh:

			// Check if default message values for timers are set, and if
			// not then set default message values.
			if sam.Message.ACKTimeout < 1 {
				sam.Subject.Event = EventNACK
			}
			if sam.Message.ACKTimeout >= 1 {
				sam.Subject.Event = EventNACK
			}

			// TODO: Make so 0 is an usable option for retries.
			if sam.Message.Retries < 1 {
				sam.Message.Retries = r.configuration.DefaultMessageRetries
			}
			if sam.Message.MethodTimeout < 1 && sam.Message.MethodTimeout != -1 {
				sam.Message.MethodTimeout = r.configuration.DefaultMethodTimeout
			}

			// --- Store the incomming message in the k/v store ---

			// Get a unique number for the message to use when storing
			// it in the databases, and also use when further processing.
			r.mu.Lock()
			dbID := r.totalMessagesIndex
			r.mu.Unlock()

			// Create a structure for JSON marshaling.
			samV := samDBValue{
				ID:  dbID,
				SAM: sam,
			}

			if r.configuration.RingBufferPersistStore {
				js, err := json.Marshal(samV)
				if err != nil {
					er := fmt.Errorf("error:fillBuffer: json marshaling: %v", err)
					r.errorKernel.errSend(r.processInitial, Message{}, er, logError)
				}

				// Store the incomming message in key/value store
				err = r.dbUpdate(r.db, r.samValueBucket, strconv.Itoa(dbID), js)
				if err != nil {
					er := fmt.Errorf("error: dbUpdate samValue failed: %v", err)
					r.errorKernel.errSend(r.processInitial, Message{}, er, logError)
				}
			}

			// Put the message on the inmemory buffer.
			r.bufData <- samV

			// Increment index, and store the new value to the database.
			r.mu.Lock()
			r.totalMessagesIndex++
			if r.configuration.RingBufferPersistStore {
				r.dbUpdate(r.db, r.indexValueBucket, "index", []byte(strconv.Itoa(r.totalMessagesIndex)))
			}
			r.mu.Unlock()
		case <-ctx.Done():
			// When done close the buffer channel
			close(r.bufData)
			return
		}

	}
}

// processBufferMessages will pick messages from the buffer, and process them
// one by one. The messages will be delivered on the outCh, and it will wait
// until a signal is received on the done channel before it continues with the
// next message.
func (r *ringBuffer) processBufferMessages(ctx context.Context, outCh chan samDBValueAndDelivered) {
	// Range over the buffer of messages to pass on to processes.
	for {
		select {
		case samDBv := <-r.bufData:
			r.metrics.promInMemoryBufferMessagesCurrent.Set(float64(len(r.bufData)))
			samDBv.SAM.ID = samDBv.ID

			// // Create a done channel per message. A process started by the
			// // spawnProcess function will handle incomming messages sequentaly.
			// // So in the spawnProcess function we put a struct{} value when a
			// // message is processed on the "done" channel and an ack is received
			// // for a message, and we wait here for the "done" to be received.

			// We start the actual processing of an individual message here within
			// it's own go routine. Reason is that we don't want to block other
			// messages to be processed while waiting for the done signal, or if an
			// error with an individual message occurs.
			go func(v samDBValue) {
				// Create a copy of the message that we can use to write to the
				// perm store without causing a race since the REQ handler for the
				// message might not yet be done when message is written to the
				// perm store.
				// We also need a copy to be able to remove the data from the message
				// when writing it to the store, so we don't mess up to actual data
				// that might be in use in the handler.

				msgForPermStore := Message{}
				copier.Copy(&msgForPermStore, v.SAM.Message)
				// Remove the content of the data field.
				msgForPermStore.Data = nil

				v.SAM.Message.done = make(chan struct{})
				delivredCh := make(chan struct{})

				// Prepare the structure with the data, and a function that can
				// be called when the data is received for signaling back.
				sd := samDBValueAndDelivered{
					samDBValue: v,
					delivered: func() {
						delivredCh <- struct{}{}
					},
				}

				// ticker := time.NewTicker(time.Duration(v.SAM.ACKTimeout) * time.Duration(v.SAM.Retries) * 2 * time.Second)
				// defer ticker.Stop()

				outCh <- sd
				// Just to confirm here that the message was picked up, to know if the
				// the read process have stalled or not.
				// For now it will not do anything,
				select {
				case <-delivredCh:
					// OK.
				case <-time.After(time.Second * 5):
					// TODO: Check if more logic should be made here if messages are stuck etc.
					// Testing with a timeout here to figure out if messages are stuck
					// waiting for done signal.
					log.Printf("Error: ringBuffer: message %v seems to be stuck, did not receive delivered signal from reading process\n", v.ID)

					r.metrics.promRingbufferStalledMessagesTotal.Inc()
				}
				// Listen on the done channel here , so a go routine handling the
				// message will be able to signal back here that the message have
				// been processed, and that we then can delete it out of the K/V Store.

				// The publisAMessage method should send a done back here, but in some situations
				// it seems that that do not happen. Implementing a ticker that is twice the total
				// amount of time a message should be allowed to be using for getting published so
				// we don't get stuck go routines here.
				//
				// TODO: Figure out why what the reason for not receceving the done signals might be.
				// select {
				// case <-v.SAM.done:
				// case <-ticker.C:
				// 	log.Printf("----------------------------------------------\n")
				// 	log.Printf("Error: ringBuffer message id: %v, subject: %v seems to be stuck, did not receive done signal from publishAMessage process, exited on ticker\n", v.SAM.ID, v.SAM.Subject)
				// 	log.Printf("----------------------------------------------\n")
				// }
				// log.Printf("info: processBufferMessages: done with message, deleting key from bucket, %v\n", v.ID)
				r.metrics.promMessagesProcessedIDLast.Set(float64(v.ID))

				// Since we are now done with the specific message we can delete
				// it out of the K/V Store.
				if r.configuration.RingBufferPersistStore {
					r.deleteKeyFromBucket(r.samValueBucket, strconv.Itoa(v.ID))
				}

				js, err := json.Marshal(msgForPermStore)
				if err != nil {
					er := fmt.Errorf("error:fillBuffer: json marshaling: %v", err)
					r.errorKernel.errSend(r.processInitial, Message{}, er, logError)
				}
				r.permStore <- time.Now().Format("Mon Jan _2 15:04:05 2006") + ", " + string(js) + "\n"

			}(samDBv)
		case <-ctx.Done():
			//close(outCh)
			return
		}
	}
}

// dumpBucket will dump out all they keys and values in the
// specified bucket, and return a sorted []samDBValue
func (r *ringBuffer) dumpBucket(bucket string) ([]samDBValue, error) {
	samDBValues := []samDBValue{}

	err := r.db.View(func(tx *bolt.Tx) error {
		bu := tx.Bucket([]byte(bucket))
		if bu == nil {
			return fmt.Errorf("error: ringBuffer.dumpBucket: tx.bucket returned nil")
		}

		type kv struct {
			key   []byte
			value []byte
		}

		dbkvs := []kv{}

		// Get all the items from the db.
		err := bu.ForEach(func(k, v []byte) error {
			va := kv{
				key:   k,
				value: v,
			}
			dbkvs = append(dbkvs, va)

			return nil
		})

		if err != nil {
			// Todo: what to return here ?
			log.Fatalf("error: ringBuffer: ranging db failed: %v", err)
		}

		// Range all the values we got from the db, unmarshal each value.
		// If the unmarshaling is ok we put it on the samDBValues slice,
		// if it fails the value is not of correct format so we we delete
		// it from the db, and loop to work on the next value.
		for _, dbkv := range dbkvs {
			var sdbv samDBValue
			err := json.Unmarshal(dbkv.value, &sdbv)
			if err != nil {
				// If we're unable to unmarshal the value it value of wrong format,
				// so we log it, and delete the value from the bucker.
				log.Printf("error: ringBuffer.dumpBucket json.Umarshal failed: %v\n", err)
				r.deleteKeyFromBucket(r.samValueBucket, string(dbkv.key))

				continue
			}

			samDBValues = append(samDBValues, sdbv)
		}

		// TODO:
		// BoltDB do not automatically shrink in filesize. We should delete the db, and create a new one to shrink the size.

		// Sort the order of the slice items based on ID, since they where retreived from a map.
		sort.SliceStable(samDBValues, func(i, j int) bool {
			return samDBValues[i].ID > samDBValues[j].ID
		})

		for _, samDBv := range samDBValues {
			log.Printf("info: ringBuffer.dumpBucket: k/v store, kvID: %v, message.ID: %v, subject: %v, len(data): %v\n", samDBv.ID, samDBv.SAM.ID, samDBv.SAM.Subject, len(samDBv.SAM.Data))
		}

		return nil
	})

	if err != nil {
		return nil, err
	}

	return samDBValues, err
}

// // printBucketContent will print out all they keys and values in the
// // specified bucket.
// func (r *ringBuffer) printBucketContent(bucket string) error {
// 	err := r.db.View(func(tx *bolt.Tx) error {
// 		bu := tx.Bucket([]byte(bucket))
//
// 		bu.ForEach(func(k, v []byte) error {
// 			var vv samDBValue
// 			err := json.Unmarshal(v, &vv)
// 			if err != nil {
// 				log.Printf("error: printBucketContent json.Umarshal failed: %v\n", err)
// 			}
// 			log.Printf("k: %s, v: %v\n", k, vv)
// 			return nil
// 		})
//
// 		return nil
// 	})
//
// 	return err
// }

// deleteKeyFromBucket will delete the specified key from the specified
// bucket if it exists.
func (r *ringBuffer) deleteKeyFromBucket(bucket string, key string) error {
	err := r.db.Update(func(tx *bolt.Tx) error {
		bu := tx.Bucket([]byte(bucket))

		err := bu.Delete([]byte(key))
		if err != nil {
			log.Printf("error: delete key in bucket %v failed: %v\n", bucket, err)
		}

		return nil
	})

	return err
}

// db update metrics.
func (r *ringBuffer) dbUpdateMetrics(bucket string) error {
	err := r.db.Update(func(tx *bolt.Tx) error {
		bu := tx.Bucket([]byte(bucket))

		r.metrics.promDBMessagesCurrent.Set(float64(bu.Stats().KeyN))

		return nil
	})

	return err
}

// getIndexValue will get the last index value stored in DB.
func (r *ringBuffer) getIndexValue() int {
	const indexKey string = "index"
	indexB, err := r.dbView(r.db, r.indexValueBucket, indexKey)
	if err != nil {
		log.Printf("error: getIndexValue: dbView: %v\n", err)
	}

	index, err := strconv.Atoi(string(indexB))
	if err != nil && string(indexB) == "" {
		log.Printf("info: getIndexValue: no index value found, probaly empty database, and no previous entries in db to process : %v\n", err)
	}

	return index
}

// dbView will look up and return a specific value if it exists for a key in a bucket in a DB.
func (r *ringBuffer) dbView(db *bolt.DB, bucket string, key string) ([]byte, error) {
	var value []byte
	// View is a help function to get values out of the database.
	err := db.View(func(tx *bolt.Tx) error {
		//Open a bucket to get key's and values from.
		bu := tx.Bucket([]byte(bucket))
		if bu == nil {
			log.Printf("info: no db bucket exist: %v\n", bucket)
			return nil
		}

		v := bu.Get([]byte(key))
		if len(v) == 0 {
			log.Printf("info: view: key not found\n")
			return nil
		}

		value = v

		return nil
	})

	return value, err

}

// dbUpdate will update the specified bucket with a key and value.
func (r *ringBuffer) dbUpdate(db *bolt.DB, bucket string, key string, value []byte) error {
	err := db.Update(func(tx *bolt.Tx) error {
		//Create a bucket
		bu, err := tx.CreateBucketIfNotExists([]byte(bucket))
		if err != nil {
			return fmt.Errorf("error: CreateBuckerIfNotExists failed: %v", err)
		}

		//Put a value into the bucket.
		if err := bu.Put([]byte(key), []byte(value)); err != nil {
			return err
		}

		//If all was ok, we should return a nil for a commit to happen. Any error
		// returned will do a rollback.
		return nil
	})
	return err
}

// startPermStore will start the process that will handle writing of
// handled message to a permanent file.
// To store a message in the store, send what to store on the
// ringbuffer.permStore channel.
func (r *ringBuffer) startPermanentStore(ctx context.Context) {

	storeFile := filepath.Join(r.configuration.DatabaseFolder, "store.log")
	f, err := os.OpenFile(storeFile, os.O_APPEND|os.O_RDWR|os.O_CREATE, 0660)
	if err != nil {
		log.Printf("error: startPermanentStore: failed to open file: %v\n", err)
	}
	defer f.Close()

	for {
		select {
		case d := <-r.permStore:
			_, err := f.WriteString(d)
			if err != nil {
				log.Printf("error:failed to write entry: %v\n", err)
			}
		case <-ctx.Done():
			return
		}
	}

}